Abstract

3-D dynamic holographic memories store information in volume holograms and allow selective erasure and rewriting. Photorefractive materials are a good candidate for dynamic holographic media in such memories. A basic problem with photorefractive holographic memories is that reading/writing/erasure of a certain hologram will also affect other stored holograms. A solution to this problem is dynamic copying [1-3]. We report here the experimental demonstration of a new dynamic photorefractive holographic memory that features simple architecture, phase coherence of holograms, system stability, and high restored diffraction efficiency. The memory system consists of a single photorefractive crystal for holographic storage and a feedback loop with a liquid crystal light valve (LCLV). The LCLV performs image amplification and thresholding. The basic idea is to reconstruct the stored weak hologram, amplify and binarize the reconstructed image with the feedback loop, and rejuvenate the ored hologram with the amplified reconstructed image as the signal beam. Both the input and the signal reconstructed from the hologram are imaged onto the writing side of the LCLV and read out from the other side. The system is stabilized by sampling the image read out from the LCLV using an array illuminator. When the reconstructed image is fed back to the writing side of the LCLV. each pixel is magnified slightly so that it is less likely to miss the reading-side pixel. Therefore, image shift due to misalignment or perturbation is corrected. Multiple holgrams are stored by scanning the angle of the reference beam. Detailed analysis and experimental results will be presented at the conference.

© 1991 Optical Society of America